Regulars

1) In India, all operators now sell 3G capable sim. Infact I dont know if there is such thing as 3G sim. Because MTNL sim which was puchased in around 2005 or so, is also 3G capable.2) No speed difference. Speed depends on dongle capacity and network operator.3) Speed should be same on 2G

whenever you go to a place where 3g signal is insufficient , your dongle switches to 2g and you can experience slower speeds.Now i myself provide universal 3g modems ie modems which go with any simcard.I use 2g loop simcard in the same dongle sometimes since i get cheaper raters but pathetic speeds.when i have to give a demo to some of my clients i use airtel/mtnl 3g.and i get good speed depending on the plan and dongle ie 3.1mbps/7.2mbps.whenever i go to my native place in goa where airtel has no 3g signal,it switches to 2g mode and i get lower speeds.

The major difference between 2G and 3G SIM cards lies within the rate of data usage and transfer. In 2G SIM cards with GPRS/EDGE, data services can transfer between 56 and 236.8 kilobits of data per second. However, 3G SIM cards can transfer 14,400 kilobits per second. This makes 3G SIM cards better for downloading data like Web pages and multimedia.

Regulars

Exactly thats what I said earlier.. there is no such thing as 2G or 3G sim card. Atleast in India it seems all operators have been giving 3G capable SIM.So its either 2G or 3G network. If u r in 3G network range u will get 3G speeds else 2G.